Materials which emit light when an electric current is passed through them are well known and used in a wide range of display applications. Liquid crystal devices and devices which are based on inorganic semiconductor systems are widely used however these suffer from the disadvantages of high energy consumption, high cost of manufacture, low quantum-efficiency and the inability to make flat panel displays, reflectance problems, i.e. low visibility in bright conditions and a narrow viewing angle e.g. +/−45°.
Organic polymers have been proposed as useful in electroluminescent devices, but it is not possible to obtain pure colours, they are expensive to make and have a relatively low efficiency.
Another compound which has been proposed is aluminium quinolate, but this requires dopants to be used to obtain a range of colours and has a relatively low efficiency.
In an article in Chemistry letters pp 657–660, 1990 Kido et al disclosed that a terbium (III) acetyl acetonate complex was green electroluminescent and in an article in Applied Physics letters 65 (17) 24 Oct. 1994 Kido et al disclosed that a europium (III) triphenylene diamine complexes was red electroluminescent but these were unstable in atmospheric conditions and difficult to produce as films.
The complexes disclosed in these articles had a relatively low photoluminescent efficiency and were only able to produce green or red light and other colours could not be produced.
We have now discovered photoluminescent and electroluminescent compounds and materials which emit blue and purplish blue light.